The objective of this project is to develop methods to detect the rare expression of LDH-C, a sperm specific isozyme; in single hepatocytes and lymphocytes of mice. The methods are to be used to measure possible changes in the frequency of LDH-X derepression that may result from exposure to environmental agents and determine correlations between increases in somatic expression of normally repressed enzymes and mutagenic or carcinogenic events. Immunofluorescent techniques have been developed to detect LDH-C in mouse hepatocytes fixed on microscope slides. The methodology is being expanded to mouse and human lymphocytes in suspension for counting on an activated cell sorter. The frequency of hepatocytes reacting with anti LDH-C has been measured in male and female DBA/2J mice and in mice exposed to procarbazine and n-ethyl-n-nitrosourea.